1. Field of the Invention
The present invention relates to a tracking controller for use in a recorded information reproducing apparatus for reading recorded information from a recording track formed on a recording medium.
2. Description of Related Art
For correctly reading recorded information from an optical disk as a recording medium, tracking control techniques are indispensable for controlling an information recording beam to follow a recording track formed on a recording surface of the optical disk.
In such a tracking control, two light detectors are disposed symmetrically to the center of the recording track for receiving reflected light when the information reading beam is irradiated to the recording disk. Then, a difference in opto-electrically transduced outputs between the two light detectors is calculated as a tracking error signal, and the position at which the information reading beam should be irradiated is adjusted to converge the signal level of the tracking error signal to xe2x80x9c0.xe2x80x9d
However, as the distance between respective recording tracks, i.e., a so-called track pitch is narrower for realizing higher density recording, the read signals are adversely affected by crosstalk from adjacent tracks, resulting in offset components superimposed on the tracking error signal. The offset components superimposed on the tracking error signal makes a smaller level difference between the tracking error signal produced when the information reading beam is in an on-track state and the tracking error signal produced when the information reading beam is in an off-track state, thereby causing a problem that a correct tracking control is prevented.
The present invention has been made for solving the problem mentioned above, and its object is to provide a tracking controller which is capable of conducting a correct tracking control even if recording tracks are formed with a narrow track pitch on a recording disk.
A tracking controller according to the present invention is intended for use in a recorded information reproducing apparatus having tracking error detecting means for detecting a tracking error based on a read signal produced by opto-electrically transducing reflected light when an information reading beam is irradiated to a recording disk, and a tracking actuator for forcing the information reading beam to follow a recording track on the recording disk based on the tracking error. The tracking controller comprises error detecting means for calculating an error value between a read signal read from a recording track intended for reading and a predetermined value, coefficient calculating means for calculating a first coefficient according to a correlation between a first read signal read from a first adjacent recording track adjacent to the recording track intended for reading on the inner peripheral side of the disk and the error value, and for calculating a second coefficient according to a correlation between a second read signal read from a second adjacent recording track adjacent to the recording track intended for reading on the outer peripheral side of the disk and the error value, and means for calculating a difference value between the first coefficient and the second coefficient as a tracking offset, and subtracting the tracking offset from the tracking error to correct the tracking offset.